System to mount electrical modules

ABSTRACT

The present invention provides a screw comprising a head and a threaded shank, wherein the shank is covered with a coating at least 60% of the length thereof from the end, the coating includes microcapsules that contain a viscous fluid with an appropriate level of viscosity. Shavings, including powdered shavings due to friction and exfoliations that may be generated during the screwing process, will be held, so that they will not fall, at the surface of the shank by the viscous fluid coming out of the microcapsules.

[0001] This application is based on application NO. 2002-193781 filed inJapan, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a screw to be screwed into aprepared hole in a workpiece, particularly to a female-thread-formationshaving holding screw that prevents shavings generated during thefemale-thread forming process from falling, when the screw is screwedinto a prepared hole inside of which female threads are already formed,as well as when the screw forms female threads while being screwed intoa prepared hole in a relatively soft workpiece.

[0004] 2. Description of the Related Art

[0005] In recent years, there is increasing need for installingelectronic device parts, and screws are often used to install parts andcovers. As a general procedure, as shown in FIG. 12, a prepared hole(not shown in the drawing) is provided in a workpiece 120, and a tappingscrew 101 is to be screwed into the prepared hole so that the threads110 on the shank 103 form the female threads 121 inside the preparedhole.

[0006] As for a material of which the workpiece 120 is made, materialsthat have relatively high recyclability are chosen in consideration oflightness in weight and environmental issues of recent years. Forexample, aluminum alloys and magnesium alloys are often used.

[0007] In particular, recently there are many items in which thosematerials are used as the following: personal computers; communicationdevices including mobile phones and the like; digital electric homeappliances including digital cameras, digital video cameras, mini discsand the like; devices related to intelligent transport systems; andautomobile parts. The workpieces made of the aforementioned materialswhich are often used in these products have tendency of becoming moreand more lightweight and compact. Also, electric circuits used as partsof electronic devices are required to be lightweight and miniaturized;accordingly, there are developments to make screws more and moreminiaturized in the present circumstances. Especially, there is anincreasing demand for applying magnesium alloys to those productsbecause of their advantageous properties such as being lightweight andenergy-saving.

[0008] When such miniaturized parts need to be fixed onto a softworkpiece, tapping screws form female threads inside prepared holeswhile being screwed into the prepared holes to fix those parts onto theworkpiece. When these female threads are formed during the screwingprocess, shavings such as powdered shavings due to friction andexfoliations are generated because of friction forces and deformation ofthe prepared holes beyond the yield point of the workpiece. Theseshavings may fall onto parts. Also the shavings sticking to the threadsmay fall when the screws are taken out of the holes. Thus, there is fearof damaging the devices or sometimes even causing a fire when theshavings fall onto an electric circuit of a printed circuit board anddevelop a short circuit.

[0009] When the workpiece is made of a soft material, during the processof forming female threads with tapping screws, normal tapping screws arelikely to suffer from friction heat due to their designs in which thewidth of each root in the threads is small. Consequently, there may be asituation where a tapping screw is burnt onto the workpiece and does notget screwed in all the way, and we may have what is called a stick-out,which means that the bearing surface of a screw head is not in contactwith the workpiece. Particularly, since magnesium alloys are soft andbrittle, fine particles are likely to be generated, and they causeadhesion in the space between the tapping screw and the threads duringthe screwing process; therefore, it is not possible to achieveself-tapping action, which means that the screw forms female threadswhile being screwed into the workpiece, and it is necessary to formfemale threads in advance inside the prepared hole.

[0010] In order to fix some parts onto a workpiece, however, even when anormal screw is screwed into the workpiece after female threads areformed in advance inside the prepared hole in the workpiece, there is apossibility that a few shavings may be generated between the screw andthe workpiece and fall, and this could still be one of the main causesof troubles in electronic devices. Moreover, since it is necessary toperform an assembly step of forming female threads in advance, themanufacturing cost increases, and a problem may arise that there is alimit to the possibility of supplying inexpensive products.

SUMMARY OF THE INVENTION

[0011] The object of the present invention is to solve the problemsmentioned above and ensure that the screwing process can be performed inan efficient manner, as well as to improve reliability in the assemblingof electronic devices by having the shavings adhered to and held by thescrew constantly, the shavings being generated during the screwingprocess.

[0012] This object can be achieved by a screw to be screwed into aprepared hole in a workpiece, comprising: a head having a drive to beengaged with a driver bit; a shank having threads and being integrallyformed with the head; and a coating covering at least 60% of a totallength of the shank, starting from an end of the shank opposite to thehead, wherein the coating includes microcapsules that contain a viscousfluid with a predetermined level of viscosity.

[0013] With this arrangement, when a part is fixed onto a soft workpiecewith a screw, even if the screw directly forms female threads whilebeing screwed into the prepared hole in the workpiece, it is possible toarrange it so that the shavings, such as powdered shavings due tofriction and exfoliations that are generated during the screwingprocess, adhere to the viscous fluid coming out of the microcapsules inthe coating, and to ensure that those shavings are held so that they donot fall from the prepared holes.

[0014] In addition, since those shavings are prevented from falling,there will be no possibility that shavings fall onto and stick toprecision electronic parts, and thus it is possible to eliminate a causeof malfunctions such as short circuits developed in the circuits ofelectronic devices and to eliminate a cause of fires. Furthermore, whenthe screw is taken out of the hole, it is also possible to prevent theshavings sticking to the threads from falling, and there will be nopossibility that a malfunction is induced at times of repairing thedevices.

[0015] It is also acceptable to have an arrangement in which part of theshank that is on the end side and includes at most one of the threads isa female-thread forming portion, wherein an included angle of the threadin the female-thread forming portion is larger than an included angle ofeach of the threads in a rod portion, which is part of the shank on thehead side, or an external diameter of the thread in the female-threadforming portion is larger than an external diameter of each of thethreads in the rod portion, or both of an included angle and an externaldiameter of the thread in the female-thread forming portion is largerthan those of each of the threads in the rod portion.

[0016] With this arrangement, it is possible to make the gap between thefemale threads and the threads of the screw relatively wide, so that theshavings come into the gap and sufficiently adhere to and are held bythe viscous fluid. In addition, it is possible to reduce resistanceagainst the screwing force during the screwing process, to reduce thefriction heat, and to obtain anti-loosening effects because theresistance is larger at the time of loosening the screw having once beenscrewed is due to the restoring force of the female threads formed inthe workpiece made of a soft material.

[0017] It is further acceptable to have an arrangement wherein thethreads each have an included angle of 50 degrees or smaller so that thewidth of each root in the threads is relatively larger, or at each ofthe threads, a pressure flank angle is smaller than a leading flankangle.

[0018] With this arrangement, when a tapping screw forms female threadsinto a workpiece made of a soft material, friction heat is less likelyto be generated, and the screw is less likely to be burnt onto theworkpiece during the screwing process, and also adhesion action isrestricted; therefore, it is possible to prevent what is called astick-out of a screw, which means that that the bearing surface of thescrew head is not in contact with the workpiece. Particularly, magnesiumalloys are soft and brittle and tend to generate fine particles, butthose fine particles will also adhere to the screw without failure;therefore, the threads on the shank and the female threads will notcause adhesion due to the friction heat during the screwing process.Thus, it is possible to have the screw form female threads while thescrew is being screwed into the workpiece, and it is not necessary toform female threads in advance inside the prepared hole. Consequently,the assembly step of forming female threads in advance becomesunnecessary, and the manufacturing cost of the products can be reduced,and it is possible to supply inexpensive products.

[0019] Here, it is desirable to have an arrangement wherein thickness ofthe coating is 30% to 90% inclusive of a height of each thread from aroot thereof.

[0020] Further, it is desirable to have an arrangement wherein theviscosity of the viscous fluid in the microcapsules is 200 cP to 500 cPinclusive.

[0021] Furthermore, it is desirable to have an arrangement wherein theviscous fluid maintains fluidity for at least six months from when thescrew is used for a first time. When fluidity is maintained for a longtime, even after the screw is screwed into the workpiece, the viscousfluid is still able to have shavings adhered thereto without becomingsolid; and thus, the screw is able to maintain the adhesive action forshavings for a long time and is reusable even when the screw is takenout of the hole and gets screwed into a workpiece again.

[0022] In addition, it is desirable to have an arrangement wherein aflash point of the viscous fluid is 260 degrees centigrade or higher.With this arrangement, even if the screw should generate heat due tofriction during the screwing process, it will not catch fire, and thesafety level is high in terms of fire prevention.

[0023] In addition, it is desirable to have an arrangement wherein theviscous fluid has copper-corrosion resistance, stress crack resistanceagainst a plastic resin member, electric non-conductance, lubricity,rust-proofing effect, and water repellency. With this arrangement, theviscous fluid does not have a bad influence on the circuit printed boardattached to the workpiece because, for example, it will not infiltrateinto the resin or make it brittle. Thus, the reliability of the productswill be improved.

[0024] Furthermore, it is desirable to have an arrangement wherein aparticle diameter of each of the microcapsules is 100 μm to 300 μminclusive. With this arrangement, most of the coating will adhere to theroots of the threads, and the microcapsules containing the viscous fluidwill also be present in abundance at the roots of the threads;therefore, it is possible to have the shavings adhered to the rootswithout failure. Also, when a normal screw having this coating isscrewed into female threads formed in advance, it is possible to have afew shavings generated between the screw and the workpiece adhered tothe coating and to eliminate a main cause of troubles of electronicdevices, in the same fashion.

[0025] Additionally, it is acceptable to have an arrangement wherein thecoating is formed by applying a coating material whose main componentsare the microcapsules, a resin binder, and a pigment.

[0026] With this arrangement, it is possible to identify each screw, andto easily distinguish the screw to be used when screws have differentcolors according to their usages, their nominal diameters, or the like.In addition, since organic solvents are not used in the coatingmaterial, which is a material used for the coating, it does not have abad influence to human bodies and the atmosphere, and it is preferablein consideration of safety and sanitary conditions and environmentalissues.

[0027] Furthermore, it is acceptable to have an arrangement wherein theworkpiece has, at an entrance of the prepared hole from which the screwenters, a counterbore having a diameter that is larger than a diameterof the prepared hole and is smaller than a diameter of the head of thescrew. With this arrangement, when a screw has once been screwed into aworkpiece and then is taken out of the hole, even if the shavingsadhered to the screw come out along with the threads, the shavings willbe collected in the counterbore; therefore, special advantageous effectscan be achieved by which, for example, the shavings including powderedshavings due to friction and exfoliations will not be scattered on theworkpiece, as well as it is possible to easily eliminate them asnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] These and other objects, advantages and features of the inventionwill become apparent from the following description thereof taken inconjunction with the accompanying drawings which illustrate a specificembodiment of the invention.

[0029] In the drawings:

[0030]FIG. 1 is a front view of the screw of an embodiment of thepresent invention;

[0031]FIG. 2 is an enlarged front view of the main structure of thescrew shown in FIG.1;

[0032]FIG. 3 is an enlarged front view of the main structure of thescrew of another embodiment of the present invention;

[0033]FIG. 4 is an enlarged front view of the main structure of thescrew of yet another embodiment of the present invention;

[0034]FIG. 5 is a cross sectional view of the main structure of thescrew in FIG. 1 to illustrate how the threads are screwed into theprepared hole;

[0035]FIG. 6 is a cross sectional view of the main structure toillustrate how asymmetric threads are screwed into the prepared hole;

[0036]FIG. 7 is a bottom view that shows another embodiment of thepresent invention;

[0037]FIG. 8 is an enlarged developed cross sectional view along theline X-X in FIG.7;

[0038]FIG. 9 is an enlarged cross sectional view to illustrate how thescrew in FIG. 2 is screwed into the workpiece;

[0039]FIG. 10 is an enlarged cross sectional view to illustrate how thescrew in FIG. 7 is screwed into the workpiece;

[0040]FIG. 11 is a cross sectional view of the main structure toillustrate how the screw of the present invention is taken out of theworkpiece; and

[0041]FIG. 12 is a cross sectional front view to illustrate how atapping screw of the prior art is screwed into a workpiece.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] The following explains embodiments of the present invention withreference to FIGS. 1 to 11.

[0043] In FIGS. 1 and 2, a tapping screw 1 comprises a head 2 and ashank 3, the shank 3 being integrally formed with the head 2 and havingthreads 10 on the external surface thereof.

[0044] A drive pit 4, which is a cross-shaped conical recess, is formedin the head 2 of the tapping screw 1 on the axial line of the shank 3,as a part of a drive of the screw to be engaged with a driver bit (notshown in the drawing). In this case, the drive is presented as the drivepit 4 being a cross-shaped conical recess; however, the drive may be asquare-shaped pit, a hexagonal-shaped pit, or a slot of other shapes, ora hole of other shapes, and is not limited as described above as long asit is in a form that is normally available.

[0045] The bearing surface 5 of the head 2 has the cylinder-shaped shank3 integrally formed therewith, the diameter of the shank 3 being smallerthan the diameter of the head 2. The shank 3 has threads 10 that areformed with a predetermined pitch. The threads 10 on the shank 3 eachhave an included angle of 50 degrees or smaller, and the pitch of thethreads 10 is made to be relatively wider so that the width of each root6 of the tapping screw 1 is relatively larger than that of a normalsmall screw.

[0046] The shank 3 includes a rod portion 7 which is on the head sideand has a constant external diameter. The shank 3 also includes afemale-thread forming portion 8 which is on the end side and is acontinuum of the rod portion 7. The included angle f of the thread inthe female-thread forming portion 8 is slightly larger than the includedangle a of each of the threads in the rod portion 7. It would bedesirable to arrange it so that these included angles α and β have aten-degree difference so that the included angle β of the thread of thefemale-thread forming portion 8 is larger. The female-thread formingportion 8 is at most one thread. The height of each of the threads 10 onthe end side of the female-thread forming portion 8 is arranged to beshorter than the height of each of the threads 10 in the rod portion 7so that, during the screwing process, the part of the screw with theshorter threads can easily go into the prepared hole (not shown in thedrawing) in the workpiece. With these arrangements, the tapping screw 1is able to mitigate, to a level as low as possible, friction caused atthe time of forming female threads 21 inside the prepared hole in theworkpiece 20 during the screwing process.

[0047] Further, in the area that is at least 60% of the length from theend of the shank 3 toward the head and all around the circumference, acoating material, which does not include organic solvents and iswater-soluble, for example, is applied so as to form a coating 9.

[0048] The coating 9 is formed so that it is adhered to the flank planes11 and the roots 6 of the threads 10. It would be best if the coating 9is adhered so as to cover 30% to 90% of the height of each threadstarting from the roots between the threads 10. The coating 9 includesmicrocapsules (not shown in the drawing) that are densely disposed, andthe microcapsules contain a viscous fluid in liquid form that maintainsfluidity (wettability) for a long time. Viscosity of the viscous fluidis 200 cP to 500 cP inclusive, which is enough for having thefemale-thread forming shavings adhered thereto. If the viscosity is at alower level than this, the coating material may drip while beingapplied, and if the viscosity is at a higher level than this, thecoating may rise between the threads too high. With the range ofviscosity mentioned above, it is possible to obtain characteristics bywhich the fluidity can be maintained for a long time even the ambienttemperature is as high as approximately 130 degrees centigrade. It wouldbe desirable if the fluidity is maintained specifically for at least sixmonths after the screw is used for the first time, and it would be moredesirable if the fluidity is maintained for about five years.

[0049] The evaporation temperature and flash point of the viscous fluidis 260 degrees centigrade or higher. This viscous fluid is superior interms of copper-corrosion resistance and stress crack resistance againsta plastic resin member. It also has electric non-conductance, lubricity,rust-proofing effect, and water repellency. In addition, the particlediameter of each of the microcapsules is 100 μm to 300 μm inclusive,which is an appropriate size for supplying a maximum amount of viscousfluid in each pitch of the tapping screw 1. The viscosity of the coatingmaterial whose main components are the microcapsules, a binder to bindthem together, and a pigment is approximately 110 cP at a normaltemperature. It is possible to color the coating material as necessarywith a colored pigment. When the coating material is colored, it ispossible to quickly recognize if the coating process has been performedon the shank 3 of the tapping screw 1 or not. When the tapping screw 1having the coating 9, which is formed by applying the coating material,is screwed into the prepared hole in the workpiece 20, the microcapsulesare ruptured by the pressure at the time of forming the female threads.Then, the viscous fluid leaks, and the shavings 23 generated during thefemale-thread forming process, including powdered shavings due tofriction and exfoliations, will adhere to and be held by the threads 10.Accordingly, when the female threads 21 are formed inside the preparedhole in the workpiece 20 by the female-thread forming portion 8 of theshank 3, as shown in FIG. 5, there will be a gap between the femalethreads 21 and the threads 10 in the rod portion 7, and thus, theshavings 23 will adhere to and be held at the gap because of the viscousfluid coming out of the microcapsules.

[0050] In addition, FIGS. 3 and 4 show examples in each of which theshape of the threads of the tapping screw 1 with the aforementionedarrangement has been slightly modified. In FIG. 3, the included angle αof each thread in the rod portion 7 is 50 degrees or smaller, which isthe same arrangement as the embodiment above, and the included angle βof the thread in the female-thread forming portion 8, which is acontinuum to the rod portion 7 and is on the end side of the shank, isthe same as the included angle α of each thread in the rod portion 7.The external diameter A of the thread in the female-thread formingportion 8 is slightly larger then the external diameter B of each threadin the rod portion 7, and the female-thread forming portion 8 is at mostone thread. With this arrangement, also, it is possible to reduce theresistance during the screwing process as mentioned earlier, and theshavings 23 will adhere to and be held by the threads 10 on the shank 3without failure because of the coating 9 applied to the threads 10. InFIG. 4, the arrangements of the female-thread forming portion 8mentioned so far are combined. Specifically, the included angle β of thethread of the female-thread forming portion 8 is arranged to be slightlylarger then the included angle α of each thread in the rod portion 7, aswell as the external diameter A of the thread of the female-threadforming portion 8 is arranged to be slightly larger than the externaldiameter B of each thread in the rod portion 7. Also with thisarrangement, it is possible to have similar effects.

[0051] Further, although the pressure flank angle is arranged to beequal to the leading flank angle at each of the threads 10 in theembodiments above, FIG. 6 shows an arrangement of threads 10 havingunequal angles, which means that, at each of the threads 10, thepressure flank angle θ1 is smaller than the leading flank angle θ2. Itis also acceptable to have an arrangement wherein the threads 10 havingunequal angles are formed in the rod portion 7, and as a continuum ofthe threads 10, the included angle β of the thread in the female-threadforming portion 8 is larger than the included angle α of each thread inthe rod portion 7 by approximately 10 degrees. It is also acceptable tohave an arrangement wherein the included angles of the threads in therod portion 7 and the female-thread forming portion 8 are equal and theexternal diameter of the thread of the female-thread forming portion 8is slightly larger than the external diameter of each thread in the rodportion 7. It is also acceptable to combine these arrangements. With anyof these arrangements, it is possible to obtain further advantageouseffects of preventing loosening.

[0052]FIGS. 7 and 8 show a non-circular shank 3 of the tapping screw 1and a developed cross sectional view of the threads 10. The threads 10are what is called trilobular threads, which means that one thread, i.e.one turn of the threads 10, includes three vertexes that each have themaximum thread radius. Between the vertexes 12, there are reliefportions 13 that each have the minimum thread radius. The crosssectional view of the threads is shown in FIG. 8, which illustrates thateach of the relief portions 13 is smaller in thickness than thethickness of the threads at those three vertexes, when compared as alocus of a circle of a constant radius from the axial point of the shank3. When the tapping screw 1 is used to form female threads 21 inside theprepared hole in the workpiece 20, those three vertexes 12 form thefemale threads 21; therefore, there will be gaps between the reliefportions 13 and the female threads 21. Since the coating 9 with the samemain components are also applied to the threads 10, the shavings 23generated during the process of forming female threads 21 with thetapping screw 1 will adhere to and be held by the relief portions 13, asshown in FIG. 10.

[0053] In addition to the shank with the arrangements mentioned above,it is also acceptable to have an arrangement wherein four grooves (notshown in the drawing) are formed in each pitch of the threads 10 on theshank 3 so that the shavings adhere to and are held by a plurality ofgrooves. With this arrangement of threads, it is also possible to have alarger quantity of shavings 23 adhered thereto and held.

[0054] When the tapping screw 1 with the arrangements so far mentionedis screwed into a prepared hole provided in advance in the workpiece 20,the threads 10 of the tapping screw 1 form female threads 21 during thescrewing process. The shavings 23 generated during this process will alladhere to and be held by the coating 9 applied to the threads 10, at theflank planes 11, the roots 6, and the relief portions 13 of each threadas well as at the grooves in some cases, as shown in FIGS. 9 and 10.With this arrangement, the shavings 23, which are generated when thetapping screw 1 is screwed into the workpiece or taken out of the hole,will not fall on the parts.

[0055] When the tapping screw 1 that once has been screwed into theworkpiece is taken out of the hole, the coating 9 applied to the shank 3of the tapping screw 1 comes up away from the female threads 21 alongwith the threads 10 while holding the shavings 23 adhered thereto. Atthis time, as shown in FIG. 11, the shavings 23 adhered to the coating 9will be collected in a counterbore 22 that is formed in advance at theentrance of the prepared hole from which the tapping screw 1 enters, andhas a diameter that is larger than the diameter of the prepared hole andis smaller than the diameter of the head of the tapping screw 1. Thus,it is possible to prevent the shavings 23 from being scattered aroundwhen the tapping screw 1 is taken out of the hole.

[0056] As additional information, in the embodiments above, the tappingscrew 1 having the threads with special arrangements is explained;however, it is also acceptable to have an arrangement wherein femalethreads 21 are formed in advance inside the prepared holes in theworkpiece 20, and the tapping screw 1 is screwed into the female threads21. In such a case, it is relatively less likely that shavings 23 aregenerated, but when the tapping screw 1 in this case also has thesimilar coating 9 applied to the shank 3, it is possible to ensure thatthe shavings 23 are prevented from falling on printed circuit boards ofelectronic devices.

[0057] Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modifications will be apparent to those skilledin the art. Therefore, unless such changes and modifications depart fromthe scope of the present invention, they should be construed as beingincluded therein.

What is claimed is:
 1. A screw to be screwed into a prepared hole in aworkpiece, comprising: a head having a drive to be engaged with a driverbit; a shank having threads and being integrally formed with the head;and a coating covering at least 60% of a total length of the shank,starting from an end of the shank opposite to the head, wherein thecoating includes microcapsules that contain a viscous fluid with apredetermined level of viscosity.
 2. The screw of claim 1, wherein partof the shank that is on the end side and includes at most one of thethreads is a female-thread forming portion.
 3. The screw of claim 2,wherein an included angle of the thread in the female-thread formingportion is larger than an included angle of each of the threads in a rodportion, which is part of the shank on the head side.
 4. The screw ofclaim 2, wherein an external diameter of the thread in the female-threadforming portion is larger than an external diameter of each of thethreads in a rod portion, which is part of the shank on the head side.5. The screw of claim 2, wherein an included angle of the thread in thefemale-thread forming portion is larger than an included angle of eachof the threads in a rod portion, which is part of the shank on the headside, and an external diameter of the thread in the female-threadingportion is larger than an external diameter of each of the threads inthe rod portion.
 6. The screw of claim 1, wherein the threads each havean included angle of 50 degrees or smaller.
 7. The screw of claim 1,wherein at each of the threads, a pressure flank angle is smaller than aleading flank angle.
 8. The screw of claim 1, wherein thickness of thecoating is 30% to 90% inclusive of aheight of each thread from a rootthereof.
 9. The screw of claim 1, wherein the viscosity of the viscousfluid in the microcapsules is 200 cP to 500 cP inclusive.
 10. The screwof claim 1, wherein the viscous fluid maintains fluidity for at leastsix months from when the screw is used for a first time.
 11. The screwof claim 1, wherein a flash point of the viscous fluid is 260 degreescentigrade or higher.
 12. The screw of claim 1, wherein the viscousfluid has copper-corrosion resistance, stress crack resistance against aplastic resin member, electric non-conductance, lubricity, rust-proofingeffect, and water repellency.
 13. The screw of claim 1, wherein aparticle diameter of each of the microcapsules is 100 μm to 300 μminclusive.
 14. The screw of claim 1, wherein the coating is formed byapplying a coating material whose main components are the microcapsules,a resin binder, and a pigment.
 15. The screw of claim 1, wherein theworkpiece has, at an entrance of the prepared hole from which the screwenters, a counterbore having a diameter that is larger than a diameterof the prepared hole and is smaller than a diameter of the head of thescrew.